Container with a reinforced base and method for manufacturing such a container

ABSTRACT

Container having a body and a bottom that together delimit an internal primary volume of the container, this container also comprising a protruding base comprising an outer wall and an inner wall, the base comprising a skirt which protrudes from the region of the join between the body and the bottom, and a foot which lies at a lower end of the skirt and defines a setting-down plane for the container, in which container: —the walls are locally welded together in the region of the skirt; —the foot forms a hollow bulge, and the outer wall, the inner wall and the setting-down plane together define a secondary volume isolated from the primary volume by the weld.

The invention relates to the field of containers, particularly bottlesor jars, manufactured by blow molding or stretch-blow molding fromparisons of plastic material such as polyethylene terephthalate (PET).

BACKGROUND OF THE INVENTION

The manufacturing of a container by blow molding consists ordinarily ofinserting into a mold, constituting the impression of the container, aparison (it can be a preform or an intermediate container obtained bypre-blow-molding of a preform), previously heated to a temperaturegreater than the glass transition temperature of the material, andconsists in injecting into the parison a fluid (particularly a gas suchas air) under pressure. The blow molding can be completed by apreliminary stretching of the parison by means of a sliding rod.

The molecular dual orientation that the material undergoes during theblow molding (axial and radial, respectively parallel and perpendicularto the general axis of the container) imparts a certain structuralrigidity to the container.

However, the requirements of the market economy, or the anti-pollutionstandards, lead manufacturers to use ever smaller amounts of material.Other things being equal, the effect of this is a reduction in themechanical performance of the containers, due in particular to a reducedrigidity of the bottom that has a tendency to collapse under thehydrostatic pressure of the contents.

For this reason, a great deal of work has been done by the manufacturerson the shape of the bottoms to increase their rigidity.

Thus, it is known to make the bottom rigid by means of ribs; see, forexample, French patent FR 2 753 435 (Sidel). This bottom keeps itsmechanical strength without being inverted as long as the conditions ofvolume and/or pressure in the container are normal. However, when theconditions are extreme, the bottom nevertheless has a tendency tocollapse.

In addition, arched bottoms, referred to as “champagne” bottoms, areknown; see, for example, French patent FR 2 730 471 or its U.S.equivalent U.S. Pat. No. 6,153,145. This type of bottom, inspired by thebottoms of glass champagne bottles, exhibits the advantage of offeringgood strength as well as good stability, but it nevertheless has thedrawback of using a large amount of material.

In practice, the most mechanically stable bottoms of containers arethose whose shape comes closest to that of a sphere because of adistribution of relatively uniform stresses. However, a container with aspherical bottom cannot be stable if it is not for that matter providedwith a base. This is why the majority of the containers with sphericalbottoms (intended particularly for carbonated beverages), generally haveadded bases (particularly by snapping-on or by gluing, see, typically,U.S. Pat. No. 4,552,275 Owens Ill.) or formed by projecting from thebottom, see U.S. Pat. No. 5,122,325 Broadway Companies.

The added bases require additional operations for manufacturing and forreprocessing waste materials, which make this type of containerundesirable in today's market. As for the bases formed by projection,they appear promising but produce manufacturing difficulties, to thepoint that, in U.S. Pat. No. 5,122,325 cited above, the base is alreadyshaped on the preform from which the container is formed. This techniqueis not without drawbacks. First, it requires an addition of material.Then, the final formation of the base during the blow molding of thecontainer is difficult to control.

Also, particularly for carbonated beverage applications, numerouspetaloid-shaped bottoms are known, comprising an alternation of valleys,of hemispheric curvature, and of projecting feet, whose ends form a seatfor the container; see, for example, French patent application FR 2 959214 or its U.S. equivalent US 2013/043255. The petaloid-shaped bottomappears as a relatively successful solution combining good resistance tostrong internal pressures in the container (because of the hemisphericcurvature of the valleys) and a relative lightness. However, thepetaloid-shaped bottom has the drawback of being rather unstable duringoperations of handling the container on the packaging lines.

SUMMARY OF THE INVENTION

An objective of the invention is to propose a manufacturing method for acontainer with an integrated base (as well as such a container) thatmeets, separately or together, the following requirements:

-   -   to offer good mechanical performance, in particular good        stability of the bottom,    -   to offer good blowability,    -   to use little material.

For this purpose, according to a first aspect, a manufacturing method isproposed for a container having a neck, a body and a bottom that jointlydelimit an inner primary volume of the container, this container furthercomprising a base, which is formed projecting from a joining areabetween the body and the bottom by a fold of material, and comprising anouter wall, formed in the extension of the body, and an inner wallformed in the extension of the bottom, the base comprising a skirt,which extends projecting from the joining area between the body and thebottom, and a foot, which extends at a lower end of the skirt, anddefines a standing plane for the container, this method being performedin a mold comprising, on the one hand, a peripheral wall, delimiting acavity whose inner surface constitutes the impression of the body of thecontainer and that of the outer wall of the base and, on the other hand,a mold bottom that has a raised surface whose shape constitutes theimpression of the bottom of the container and of the inner wall of thebase and that works with an open end of the cavity, the mold bottom andthe peripheral wall being mounted to move in relation to one anotherbetween an initial position, in which the raised surface is separatedfrom the cavity, and a final position, in which the raised surfaceblocks the opening of said end to complete the impression of thecontainer, this method comprising the operations consisting in:

-   -   inserting a previously heated parison into the mold while the        mold bottom and the peripheral wall are in the initial position,    -   injecting a pressurized fluid into the parison,    -   placing the mold bottom and the peripheral wall in the final        position, to bring about said fold of constituent material of        the skirt,    -   extracting the thus formed container from the mold,    -   locally welding (particularly ultrasonically—as a variant, the        welding can be performed by other techniques such as laser or        radiofrequency) the outer wall and the inner wall of the base in        the area of the skirt, within a welding device that is separate        from the mold.

Such a welding makes it possible to make the base rigid, for the benefitof the stability of the container obtained. The blowability of thecontainer is not affected by this technique, which furthermore does notrequire additional material.

According to a second aspect, a container is proposed that is obtainedby blow molding or stretch-blow molding from a parison of plasticmaterial, this container having a neck, a body, and a bottom thatjointly delimit an inner primary volume of the container, this containerfurther comprising a base, which is formed projecting from a joiningarea between the body and the bottom by a fold of material, andcomprising an outer wall, formed in the extension of the body, and aninner wall, formed in the extension of the bottom, the base comprising askirt, which extends projecting from the joining area between the bodyand the bottom, and a foot, which extends at a lower end of the skirtand defines a standing plane for the container, a container in which:

-   -   the walls are locally welded to one another in the area of the        skirt;    -   the foot forms a hollow bulge, the outer wall, the inner wall        and the standing plane that jointly define a secondary volume        that is isolated from the primary volume by the welding.

The skirt, for example, is in the shape of a truncated cone or isannular.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will be brought out in thedescription of an embodiment, given below with reference to theaccompanying drawings in which:

FIG. 1 is a bottom perspective view of a container with an integratedbase;

FIG. 2 is a partial radial cutaway view of the container of FIG. 1;

FIG. 3 is a detail view, on an enlarged scale, of the container of FIG.2, taken from the insert III;

FIG. 4 is a view similar to FIG. 3, according to a variant embodiment;

FIG. 5 is a cutaway view showing a a mold for the manufacture of thecontainer of FIGS. 1 and 2, equipped with a wall and a mold bottom thatis mounted to move relative to the wall between a low position (asillustrated in FIG. 5) and a high position;

FIG. 6 is a detail view of the mold of FIG. 6, showing, on the left, thelow position of the mold bottom and, on the right, the high position ofthe mold bottom;

FIG. 7 is a detail cutaway view illustrating a welding operationperformed on the base.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Throughout this description, as well as, where appropriate, in theclaims, the terms “lower,” “upper,” “top,” “bottom,” etc., are used withreference to the drawings for greater ease of understanding. They mustnot be understood as being limitations of the scope of the invention,particularly regarding the orientation of the containers or molds fortheir manufacture. Actually, the vertical orientation of the axis of thecontainers and the corresponding orientation of the manufacturing molds,with the mold bottoms located below the mold part or parts being usedfor the molding of the body of the containers, is only one preferredembodiment.

Shown in FIG. 1 is a container 1, in this particular case a bottle, madeby blow molding or stretch-blow molding from a parison 2 (in this case apreform) of thermoplastic material, in this case of PET (polyethyleneterephthalate).

This container 1 comprises, at an upper end, a neck 3 that opens towarda rim 4. In the extension of the neck 3, the container 1 comprises inits upper part a shoulder 5 that flares out in the direction opposite tothe neck 3, this shoulder 5 being extended by a lateral wall or body 6,with a generally rotationally-cylindrical shape around a main axis X ofthe container 1 (illustrated in FIG. 5).

The container 1 further comprises a bottom 7 that extends away from theneck 3, from a lower end of the body 6 that constitutes a joining area 8between the body 6 and the bottom 7. As in the illustrated example, thejoining area 8 between the body 6 and the bottom 7 can be narrowedrelative to the rest of the body 6. According to a particularembodiment, the diameter measured in the area of the lower end of thebody 6, at the site of the joining area 8 with the bottom 7, is, forexample, about ⅘ of the overall diameter of the body 6.

In the example illustrated, the bottom 7 comprises an arch 9 thatextends from the joining area 8 up to a central area 10 forming aprojection toward the interior of the container 1 in the direction ofthe axis X. According to an embodiment illustrated in FIG. 2, the arch 9is concave and faces toward the interior of the container 1. As avariant, however, the arch could be concave and face outward.

The body 6 and the bottom 7 together delimit an inner primary volume 11of the container 1, into which the contents (typically a liquid,particularly a beverage, which can be carbonated) of the container 1 areintended to be introduced.

As is seen in the figures, the container 1 further comprises a base 12that is formed projecting from the joining area 8, at the lower end ofthe body 6, by a fold of material that is produced by blow molding. Itis by this base 12 that the container 1 can rest on a flat surface suchas a table.

The base 12 exhibits a double thickness and comprises an outer wall 13,formed in the extension of the body 6, and an inner wall 14 formed inthe extension of the bottom 7 and folded against the outer wall 13.

More specifically, the base 12 comprises, in the first place, a skirt15, which extends projecting from the joining area 8, and a foot 16,which extends at a lower end of the skirt and defines an annularstanding plane 17 for the container 1.

According to an embodiment illustrated in FIGS. 2 and 3, the skirt 15has an approximately conical shape that is flared outward from thecontainer 1 (in other words, downward). According to a variantembodiment illustrated in FIG. 4, the skirt 15 is annular and extendsapproximately in the manner of a collar around the axis X.

As is seen clearly in FIGS. 3 and 4, the foot 16 forms a hollow bulge inradial projection opposite the axis X. In other words, the foot 16 formsapproximately a circular ring around the axis X, with a radialcross-section approximately in the shape of a d (as shown in FIGS. 3 and4). In this way, the outer wall 13, the inner wall 14, and the standingplane 17, while extending in a transverse plane that is perpendicular tothe axis X ensuring the junction between them, jointly define asecondary volume 18.

In the area of the skirt 15, the outer wall 13 and the inner wall 14 arein mutual contact. More specifically, the outer wall 13 and the innerwall 14 are locally welded to one another in the area of the skirt 15 bya weld 19. This weld 19 can be a spot weld made, for example, halfway upthe skirt 15, or a weld that extends over a more extensive surfacebetween a surrounding area of the joining area 8 between the body 6 andthe bottom 7 and a surrounding area of the junction between the skirt 15and the foot 16.

The weld 19 can form a local bond between the material of the outer wall13 and that of the inner wall 14, thus forming locally, in the area ofthe skirt 15, a single body, or else be an annular weld extending to theinterface between the outer wall 13 and the inner wall 14.

In the foot 16, however, the outer wall 13 and the inner wall 14 areseparated from one another to form the secondary volume 18 in which atoroidal air bubble is trapped. This air bubble, trapped in the foot 16during blow molding, is at a pressure that is higher than or equal tothe atmospheric pressure. However, since the weld is, as we will see,produced by an additional operation after the blow molding, a relativeequalization of the pressures between the primary volume 11 and thesecondary volume 18 can occur during the degassing of the container 1following the blow molding, by a release at the interface between theouter wall 13 and the inner wall 14 before their welding.

The welding 19 contributes to making the skirt 15 (and therefore thebase 12) rigid by preventing the sliding of the walls 13, 14 over oneanother. A better mechanical strength of the bottom 7 and a slighterrisk of inverting it in particular results from it.

By its shape, the foot 16 offers a relatively wide standing plane 17,favorable for good stability of the container 1. Further, the bulge ofthe foot 16, by its rounded shape, facilitates the conveying of thecontainer 1 over any type of conveyor (belt, roller) and limits therisks of wedging of the base 12 in the gaps between adjacent conveyorelements.

In FIGS. 5 and 6, a mold 20 for the manufacture by blow molding orstretch-blow molding of the container 1 from a parison 2 (in this case apreform) has been shown.

This mold 20 comprises a peripheral wall 21, defining a cavity 22, thatconstitutes the impression of the body 6 of the container 1 and that ispierced with an opening 23 at one end, and opposite the opening, a moldbottom 24 having a raised surface 25 whose shape constitutes theimpression of the bottom 7 of the container 1. The mold bottom 24 andthe peripheral wall 21 are mounted to move in relation to one anotherbetween an initial position, in which the raised surface 25 is separatedfrom the cavity 22, and a final position, in which the raised surface 25blocks the opening 23 to complete the impression of the container 1.

In the preferred embodiment, illustrated in FIG. 5, in a way known inthe art, the peripheral wall 21 is made up of at least two mating parts21A, 21B (known by the name of half-molds or half-shells), which eachdefine a portion of the cavity 22. The two parts can be separated fromone another during the insertion of a preform and during the withdrawalof a container, even though they are flattened against one another toform the cavity 22 during the manufacture.

The mold 20 is oriented along a vertical axis, corresponding to that ofthe container 1, and the container 1 is formed neck up. To do this, thecavity 22 is oriented with its opening 23 downward, and the mold bottom24 is found in the area of the opening 23 of the cavity 22, with theraised surface 25 oriented upward, therefore toward the interior of thecavity. Further, to impart the relative mobility of the mold bottom 24and the peripheral wall 21, it is the mold bottom 24 that is mounted tomove in relation to the peripheral wall 21 between a low position(illustrated in FIG. 5 and on the left in FIG. 6), in which the raisedsurface 25 is separated from the cavity 22, and a high position, inwhich the raised surface 25 blocks the opening 23 to complete theimpression of the container 1.

As can be seen in FIG. 6, the peripheral wall 21 defines, beyond theopening 23, an inner peripheral surface 26 constituting the impressionof the outer wall 13 of the base 12, including a truncated cone-shapedupper cross-section 27 constituting the outer impression of the skirt 15and a toroidal lower cross-section 28 constituting the impression of thebulge of the foot 16. In a complementary manner, the mold bottom 24exhibits, in the extension of its raised surface 25, an outer peripheralsurface 29 constituting the impression of the inner wall 14 of the base12, including a truncated cone-shaped upper cross-section 30constituting the outer impression of the skirt, and an annular lowercross-section 31 constituting the impression of the standing plane 17.

The container 1 is formed in the following manner. The parison 2 isfirst inserted into the mold 20 after having been previously heated to atemperature greater than the glass transition temperature of thematerial (or about 80° C. for PET). The parts 21A and 21B are thenseparated, and the mold bottom 24 is in low position. Then, the parts21A and 21B are brought together to form the cavity 22.

A pressurized fluid (particularly air) is then introduced into theparison 2 to form the container 1 by blow molding. The materialundergoes an expansion (optionally accompanied by a stretching, by meansof a stretching rod, not shown) in the cavity 22 until coming in contactwith the peripheral wall 21 and with the raised surface 25 of the moldbottom 24, the mold bottom being kept in low position.

Under the pressure of the blow molding, the material then flows into thevolume made between the inner peripheral surface 26 and the outerperipheral surface 29. At a predetermined time, the mold bottom 24 ismoved to its high position, which brings the material of the bottom 7 toits final shape and position and forms the base 12 by pinching thematerial in the area of the skirt 15, although no welding of thematerial in the skirt 15 results, the PET not making it possible toperform a welding by simple contact at the temperatures used for theblow molding, in contrast to PVC, for example.

Once the container 1 is formed, it is extracted from the mold 20, and anadditional welding operation is performed in the area of the skirt 15.This welding is performed by means of a welding device 32 that isseparate from the mold 20.

According to a particular embodiment, illustrated in FIG. 7, the weldingis performed ultrasonically. The device 32 is then an ultrasonic weldingdevice, which comprises a sonotrode 33 connected to a converter 34 ofelectrical energy into mechanical energy, applied against the inner wall14 in the area of the skirt 15, and a contact anvil 35 applied on theother side against the outer wall 13, also in the area of the skirt 15.The ultrasonic vibrations of the sonotrode sufficiently heat thematerial at the interface between the outer wall 13 and the inner wall14 to form their local bond.

As a variant, the welding can be performed by means of a laser beam(laser welding), or else by means of a radiofrequency field (also calledhigh-frequency welding), the latter being particularly suited topolymers such as PET.

Further, although the welding operation described above is applied to abase 12 comprising a hollow foot 16 defining a secondary volume 18, thiswelding can be applied to a base whose foot would be solid, i.e., thisfoot would be formed by a lower end of the walls 13 and 14 that would bein contact with one another up to the standing plane 17.

1. A container (1) obtained by blow molding or stretch-blow molding froma parison (2) of plastic material, said container (1) comprising: a neck(3), a bottom (7), and a body (6) between the neck (3) and the bottom(7) and connecting the neck (3) with the bottom (7), the neck (3) thebody (6) and the bottom (7) jointly delimiting an inner primary volume(11) of the container (1); and a base (12) projecting from a joiningarea (8) where the body (6) joins with the bottom (7), the base (12)formed of a fold of material that includes an outer wall (13) formedfrom an extension of the body (6), and an inner wall (14) formed from anextension of the bottom (7), the base comprising a skirt (15) where theouter wall (13) and the inner wall (14) extend from the joining area andare in mutual contact with each other, and a foot (16) that extends froman end portion of the skirt (15) and contains a hollow bulge in which anair bubble is trapped, the foot (16) defining a standing plane (17) forthe container (1), wherein the inner and outer walls (13, 14) are weldedto one another at a portion of the skirt (15) between the joining area(8) and a junction of the skirt (15) with the foot (16), and wherein thebottom (7) of the container, from the joining area (8) to a central area(10) surrounded by the joining area (8), forms an arch that is concavefacing an interior of the container.
 2. The container according to claim1, wherein the skirt (15) has a shape of a truncated cone.
 3. Thecontainer according to claim 1, wherein the skirt (15) is annular.